Magnetic core for electrical machinery



May 17, 1927. 1,629,311

w, E. RUDER MAGNETIC CORE FOR ELECTRICAL MACHINERY Filed March 12, 1925 Fig.2.

Inventor-'1 Wi liam E. Ruder",

His Attorney Patented May 17, 1927.

UNITED STATES PATENT OFFICE.

WILLIAM E. RUDER, OF SCHENECTADY, NEW YORK, .ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A COEPDRATION OF YORK.

MAGNETIC GORE FOR ELECTRICAL MACHINERY.

Application filed March 12, 1925. Serial No. 15,048.

The present invention relates to the constructionof magnetic cores for transformers, dynamo-electric machinery and other electric apparatus.

It is the object of my invention to provide a construction whereby the energy losses due to eddy currents in magnetic cores will be reduced, with a consequent increase in the efiiciency of operation of the devices of which the cores form a part.

Heretofore the laminations of which the cores of magnetic devices are constituted have been provided with a thin, coating of varnish consisting of a gummy or resinous material for the purpose of insulatin the laminations from each other. I have that these materials tend to flow when subjected to the heavy pressures used in assembling large magnetic cores, thus partly destroying their insulatingvalue by bringing the laminations intoelectrical contact wherever the varnish has been displaced. When the scale which is formed on the lamination's during their manufacture is removed before coating then the insulating value of a varnish on the sheets is even less effective, and the eddy current losses hence are high.

Ordinary electrical'insulation cannot be interposed between the laminations as this would increase the bulk of the core and thus offset any gain in efliciency due todecreased' eddy current losses.

I have discovered thatthe laminations of I a core may be effectively insulated. by providing the laminations with a thin coating of varnish in which a finel divided solid insulating material has een incorporated, thus producing a film which will not flow under pressure.

The accompanying drawing shows in Fig. 1 a transformer core as illustrative of the class ofap'paratus to which my invention is applicable; Fig. 2 showing a single sheet or lamination of the core.

' In; carrying out my invention the sheet material which is to be built u into the cores, for example, silicon steel s eats, such ound as shown in Fig. 2, are provided with the desired coating by spraying,painting or by passing through rubber rollers upon which the coating material is applied. Linseed oil, bakelite or other suitable hardening adhesive material into which has been incorporated a substantial proportion, say 20 per cent by weight, of finely divided china clay, silica, mica or other solid insulating material provides a suitable product, The light flaky product. obtained by heating phlogopite, a magnesia mica mined at Libby, Montana, makes a desirable filler. Mixtures of difi'erent insulating materials sometimes may be used to advantage.

The coated material is baked to set the binder and then is assembled in the usual manner, to form a core such as shown in Fig. 1. The resistance of magnetic cores thus provided with a non-flowing coating is enormously higher than the resistance of a core provided with ordinary varnish.v The increase of resistance varies widely irom a thousand fold to a hundred thousand fold. The eddy current losses of magnetic cores comprising laminations when coated with a non-flowing material are reduced fifty per cent or even more depending on the nature of the material.

- .What I claim as, new and desire to secure by Letters Patent of the United States, is

1. An article of manufacture comprising magnetic sheet material provided with a thin, adherent, electrical insulating, and heat resisting coatin said coating -containmg varnish and a sidistantial proportion of finely'divided mica.

2. magnetic core for electrical devices comprising aplurality of laminations. of magnetic material, the laminations being provided with thin films of adherent insulat- 1n r material, said insulating material contaming approximately 20 per cent by weight of finely divided mineral insulation, and being capable of withstanding pressure. In witness whereof, I have hereunto set my hand this 11th day of March. 1925.

' WILLIAM E. RUDEB. 

